1. Field of the Invention
The present invention relates to an image determining method and an image sensing apparatus, and particularly relates to an image determining method and an image sensing apparatus which can determine if the object image is a front image or a rear image.
2. Description of the Prior Art
More and more electronic apparatuses can be controlled by a gesture. For example, if a television is in a sleep state and the user stands in front of the television and makes a fist, the television is activated. For another example, if the television is operating and the user stands before the television and waves, the television switches the displayed channel. A camera is always provided for such function, which is applied to capture images ahead of the television to determine if any user's action matches the pre-determined gesture. However, if the real user's image and the rear image cannot be accurately distinguished, the gesture may be mis-determined.
FIG. 1 is a schematic diagram illustrating the gesture may be mis-determined while a gesture is applied to control the electronic apparatus, for prior art. As illustrated in FIG. 1, the above-mentioned camera 100 always comprises an image sensor IS and a lens L. The image sensor IS captures an image via the lens L. As above-mentioned, the captured image must be accurately determined to check if it is a real user's image or a rear image, or the gesture cannot be correctly determined. One common method is determining an image closer to the electronic apparatus as a front image, which is applied as a basement for determining a gesture. Also, an image faraway from the electronic apparatus is determined as a rear image, which is not applied as a basement for determining the gesture. The reason for determining an image far away from the electronic apparatus as the rear image is that the user is always close to the electronic apparatus while performing a gesture to control the electronic apparatus. By this way, the gesture can be accurately determined. On the opposite, if such mechanism is not applied, a far image may be applied as abasement for determining a gesture of the user.
Please refer to FIG. 1 again. The lens L comprises a focal point F and a corresponding focal distance FD. The above-mentioned determining steps for determining the front image and the rear image determines the image inside the focal distance FD (ex. the hand image H1) as a front image, and determines the image outside the focal distance FD (ex. the hand image H2) as a rear image.
Many methods can be applied to determine a distance for the object. For example, time-of flight or structured lighting can be applied to determine a distance for the object. However, such methods have some issues, for example, the power consumption is high or the distance for the object cannot be determined if the object is too close to the image sensor.